In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Pat. No. RE 33,949, the contents of which are incorporated herein by reference.
In longitudinal recording, fringe fields can be produced that can inadvertently write or erase data on adjacent parallel tracks on the disk. In order to not write or erase data in adjacent tracks, the fringing field in the media in the adjacent track should be less than the nucleation field. Furthermore, in order to have a good write process, the write field in the media in the desired track for writing data should be at least twice the coercivity of the media.
Typically, the write coil is overdriven with current in order to quickly change the magnetic data in the media. For example, the profile of a current signal to the write coil may include a brief pulse of 100 milliamps and settling down to a signal of 30 milliamps. Unfortunately, overdriving the write coil in this manner ends up overdriving the fringe field as well. Of course, this can end up causing fringe or adjacent track erasure (ATE). It may be that only a few bits on an adjacent track are erased on each pass, but after writing to a particular track 100 times or more, then the adjacent track ends up corrupted. It should be understood that there are some applications where a particular track could be written to millions of times.
Previous approaches to reduce ATE have related primarily to moving sharp edges on the larger write pole further from the gap between the write poles. As is well known, the two write poles (commonly referred to as P1 and P2) are typically of different width with P2 being on the order of magnitude of the track to be written and the majority of P1 being significantly wider. The corners of P1 closest to P2 have been found to be the most problematic in creating fringing fields, since sharp edges typically cause fields to concentrate there. As shown in U.S. Pat. No. 5,267,112, these front corners of P1 can be beveled off. In this manner there are still corners, but they are further from the gap so there is less ATE. It should be noted that because of the non-linear magnetic characteristics of the recording media, reducing the fringing fields by as little as 10% can significantly reduce ATE.
Another technique for reducing ATE is now a part of the typical process of manufacturing GMR read/write heads. This technique includes using the P2 write pole as a mask on P1 and ion milling away the upper surface of P1. This ion milling process moves the corners further from the gap between P1 and P2. The ion milling that creates this deep cut does, however, have the disadvantages of cutting away the top and sides of P2 and consequently reducing track width control, creating a flux bottleneck in P2, and requires a lengthy ion milling process which results in undesirably long process times.
In addition, increasing the depth of the ion milling on P1 has diminishing returns on ATE. This is because the fringing fields come not only from the portions of P1 that are closest to P2 yet not in the gap. In addition, fringing fields come from other sources, such as the write coil, other portions of P2, and so forth.
It has also been discovered that the relationship between the magnetic field and magnetization of the media changes with temperature, so that what might be an acceptable amount of fringing field at room temperature becomes a problematic amount of fringing field at elevated temperatures.
It is desirable to design/provide a read/write head which does not suffer from the above drawbacks. It is against this background and a desire to improve on the prior art that the present invention has been developed.